An Organic Light-Emitting Diode (OLED) is an active light-emitting device. As compared with Thin-Film-Transistor Liquid Crystal Display (LCD) and Plasma Display Panel (PDP) in the prior art of panel display technologies, organic light-emitting display devices using Organic Light-Emitting Diodes, as one of the technologies that have received the most attention in the panel display technology field, have advantages such as high contrast ratio, wide viewing angle, low power consumption and thinner volume, and are expected to become the next-generation mainstream panel display technology.
An OLED device mainly comprises an anode, an organic light-emitting layer and a cathode arranged in a stacked manner. In order to increase the electron injection efficiency, the OLED cathode is supposed to use a metal material having its work function that should be as low as possible, and because electrons are more difficult to be injected than holes, the level of work function of the metal seriously affects the light-emitting efficiency and service life of an OLED device, lower work function of the metal may achieve easier electron injection, so as to achieve higher light-emitting efficiency. Besides, lower work function may achieve lower barrier potential of the organics-metal interface, so as to achieve less Joule heat produced during work, thus, the service life of the device may be largely increased.
However, a single-layered metal cathode with a low work function, such as Mg, Ca, easily becomes oxidized in air, which causes instability of the device and shortens the service life, therefore, an alloy of metal with a low work function and anti-corrosion metal is usually selected to alleviate this problem. When cathode film made of a single metal is evaporation-plated, a lot of morphology defects or structural defects would be formed, which leads to deterioration of the oxidative resistance thereof. When an alloy cathode is evaporation-plated, a small amount of metal having relatively active chemical property would preferentially diffuse into the defects, which makes the film structure more complete, so as to make the entire cathode layer stable.
However, in actual use, the above-mentioned alloy cathode structure still has relatively poor stability. Research has proven that, the alkali metal forming the cathode's alloy would still reacts with water and oxygen in the air, which lowers the light-emitting efficiency of the device, and in the meantime the alkali metal would easily diffuse into the light-emitting layer and causes quenching of luminescence.